Cultural importance 
For humans, the head and particularly the face are the main distinguishing feature between different people, due to their easily discernible features such as hair and eye color, nose, eye and mouth shapes, wrinkles, etc. The human head typically weighs between 5 and 30 lbs. Human faces are easily differentiable to us due to our brains' predispositions toward discriminating human facial forms. When observing a relatively unfamiliar species, all faces seem nearly identical, and human infants are biologically programmed to recognize subtle differences in anthropic facial features.
People who are more intelligent than normal are sometimes depicted in cartoons as having bigger heads, as a way of indicating that they have a larger brain; in science fiction, an extraterrestrial having a big head is often symbolic of high intelligence. Outside of this symbolic depiction, however, advances in neurobiology have shown that the functional diversity of the brain means that a difference in overall brain size is not a reliable indicator of how much, if any, difference in overall intelligence exists between two humans.
The head is a source for many metaphors and metonymies in human language, including referring to things typically near the human head ( "the head of the bed"), things physically similar to the way a head is arranged spatially to a body ("the head of the table"), metaphorically ("the head of the class/FBI"), and things that represent some characteristic we associate with the head, such as intelligence ("there are a lot of good heads in this company"). These examples are all from English, but only some are possible expressions in other languages (depending on the language). (See Lakoff and Johnson 1980, 1999)
In many cultures, covering the head is seen as a sign of respect. Often, some or all of the head must be covered and veiled when entering holy places, or places of prayer. For many centuries, women in Europe, the Middle East, and South Asia have covered their hair as a sign of modesty. This trend has changed drastically in Europe in the 20th century, although is still observed in other parts of the world. In addition, a number of religious paths require men to wear specific head clothing—such as the Islamic Taqiyah, Jewish yarmulke, or the Sikh turban; or Muslim women, who cover their hair, ears, and neck with a scarf.
People may cover the head for other reasons. A hat is a piece of clothing covering just the top of the head. This may be part of a uniform, such as a police uniform, a protective device such as a hard hat, a covering for warmth, or a fashion accessory.
Different headpieces can also signify status, origin, religious/spiritual beliefs, social grouping, occupation, and fashion choices.
A study in the United States estimated the average human head circumference to be 53 cm in females and 57 cm in males.
See also 
- Campbell, Bernard Grant. Human Evolution: An Introduction to Man's Adaptations (4th edition), ISBN 0-202-02042-8